Power Electronics

Class D Audio Amp Suits Portables

Analog Devices has introduced two Class-D audio amplifiers designed to meet the low-power, small size, and growing sound quality requirements of portable electronics. ADI is applying Class-D amplifier design experience to address the space constraints and battery-consumption requirements of handheld devices, such as cellular handsets.

ADI’s SSM2301 and SSM2304 Class D amplifiers are designed to efficiently drive speakers in handheld and portable consumer applications by consuming minimal power, employing sigma-delta modulation to reduce electromagnetic interference (EMI) emissions, and integrating a filterless topology that eliminates external components.

The SSM2301 (mono) and SSM2304 (stereo) devices operate at a very high 85% efficiency over a wide range of output power levels. The SSM2301 delivers 1.4 W into an 8-Ω load, and the SSM2304 delivers 2 W of power into a 4-Ω load. Both devices operate on a single 2.5-V to 5.5-V supply, have a micro-shutdown mode with a maximum shutdown current of 20-nA, and feature a built-in thermal shutdown and output short circuit protection.

The amplifiers are housed in 8-lead, 3-mm × 3-mm lead-frame chip-scale packaging (LFCSP). Board space is further conserved with a filterless topology that eliminates external output filters.

The SSM2301 and SSM2304 have less than 1% total harmonic distortion plus noise (THD+N) when driving peak output loads from a 5-V supply, and a signal-to-noise ratio (SNR) that is better than 98 dB. The fully-differential input provides excellent rejection of common-mode noise on the input. The amplifiers also include click-and-pop suppression circuitry that reduces audible noise on activation and deactivation—and feature flexible fixed and user-adjustable gain configurations.

The SSM2301 and SSM2304 Class-D audio amplifiers are sampling now, with production quantities available in August 2006, and are priced at $0.55 per unit in 1000-piece quantities. An evaluation board with additional measurement filters is also available.

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